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I hope you can save the fish. regular large water changes are essential at this point. and you really need that API liquid test kit otherwise you will never know what your ammonia and nitrites are reading
good luck

5 rosy barbs, 3 female, 2 male
2 Opaline Gourami, one male, one female (they get along great)
3 neon tetra, small school but stick together well, had them for ~3 months, doing well.
1 albino cat
upside down cat died this morning, they were my 2 bottom feeders.
And one African Dwarf frog, makes it's appearances once every so often, I have thought it had died several times because it disappears frequently. Had it for over a year.

Other misc info:
~10 live plants
a few artificial just to flesh out the vegetation, hopefully will replace soon with more live.
I use an LED light rather than the tube
temp ~78*- 82* depending on room temp
1 large air stone beneath substrate

A 75 gal with eight Discus, fake plants, and a lot of wood also with sand substrate. Clean up crew is down to just two Sterba's Corys. Filters: continuous new water flow; canister w/UV, in-tank algae scrubber!! Finally, junked the nitrate removal unit from hell.

Just to be absolutely certain, are you treating the tap water prior to adding it to the tank? If not then all this advice about cycling and filter maintenance is irrelevant.

I use a de-chlorination product and follow the instructions on the bottle for the amount treated. I also use Melafix, a teetree oil extract which is said to calm the fish and help with bacterial build up, I add only about 1/4 of what is recommended on the bottle for this. But here's an update for you guys:
I did the large water change, fish looking healthier and happier, got the API test kit the following day, only last night got chance to run a test (about 4 days since water change) and so, because it was late at night (I'm a full time student w/ 2 part time jobs, time doesn't come easy to me :]) I only tested the Nitrates. They were red, like bright red, so I'm doing a water change today as soon as I get back from class here in about 2 hours.